Most drugs are absorbed from small intestine but some are absorbed from stomach and colon. On oral administration, drug action has a slower onset and more prolonged but less potent effect than when drugs are given parenterally. The thin epithelium and the rich capillary network under the tongue permit rapid absorption and drug action. In addition, the drug is saved from hepatic inactivation and destruction by digestive enzymes as it reaches the general circulation without transverse through the liver.
Rectal administration can be advantageous when the stomach is retentive due to vomiting, when the drug has objectionable taste or odor or when it can be destroyed by digestive enzymes. Parenteral route refers to any route other than gastrointestinal, but is commonly used to indicate subcutaneous, intramuscular and intravenous injections. These routes may be selected when the drug is poorly absorbed from the gut or inactivated by digestive enzymes or metabolized during its passage through liver or if the patient is unable to take or tolerate oral medication or if a rapid effect is desired.
Drugs in solution are administered parenterally by means of a syringe — needle unit or an intravenous infusion set. In Intradermal injections the drug is injected into the outer layers of the skin. The amount of drug is small and absorption is slow. This route is mainly used for diagnostic tests and it is also used for injecting BCG vaccine. Subcutaneous injections are made into the loose subcutaneous tissue under the skin.
This route is used to inject small amount of drug 2 ml or lesser. Drug absorption is slower and drug action is longer. This route is not advised in shock states because the reduced peripheral circulation may decrease the absorption rate.
Irritant drugs are not given subcutaneously as they are painful and may cause tissue necrosis. Hypodermoclysis is a form of subcutaneous injection that permits the slow administration of large amounts — ml in adults of fluid such as isotonic saline or glucose solution. Drugs used to treat ear inflammation and infection can be applied directly to the affected ears.
Ear drops containing solutions or suspensions are typically applied only to the outer ear canal. Before applying ear drops, people should thoroughly clean the ear with a moist cloth and dry it. Unless the drugs are used for a long time or used too much, little of the drugs enter the bloodstream, so bodywide side effects are absent or minimal.
Drugs that can be given by the otic route include hydrocortisone to relieve inflammation , ciprofloxacin to treat infection , and benzocaine to numb the ear.
If a drug is to be breathed in and absorbed through the thin mucous membrane that lines the nasal passages, it must be transformed into tiny droplets in air atomized. Once absorbed, the drug enters the bloodstream. Drugs administered by this route generally work quickly. Some of them irritate the nasal passages.
Drugs that can be administered by the nasal route include nicotine for smoking cessation , calcitonin for osteoporosis , sumatriptan for migraine headaches , and corticosteroids for allergies. Drugs administered by inhalation through the mouth must be atomized into smaller droplets than those administered by the nasal route, so that the drugs can pass through the windpipe trachea and into the lungs. How deeply into the lungs they go depends on the size of the droplets.
Smaller droplets go deeper, which increases the amount of drug absorbed. Inside the lungs, they are absorbed into the bloodstream. Relatively few drugs are administered this way because inhalation must be carefully monitored to ensure that a person receives the right amount of drug within a specified time.
In addition, specialized equipment may be needed to give the drug by this route. Usually, this method is used to administer drugs that act specifically on the lungs, such as aerosolized antiasthmatic drugs in metered-dose containers called inhalers , and to administer gases used for general anesthesia.
Similar to the inhalation route, drugs given by nebulization must be aerosolized into small particles to reach the lungs. Nebulization requires the use of special devices, most commonly ultrasonic or jet nebulizer systems.
Using the devices properly helps maximize the amount of drug delivered to the lungs. Drugs that are nebulized include tobramycin for cystic fibrosis Cystic Fibrosis CF Cystic fibrosis is a hereditary disease that causes certain glands to produce abnormally thick secretions, resulting in tissue and organ damage, especially in the lungs and the digestive tract Pneumonia is one of the most common causes of death worldwide.
Often, pneumonia is the final Coughing, wheezing, and shortness of breath that occur in response to specific triggers are Side effects can include those that occur when the drug is deposited directly in the lungs such as cough, wheezing, shortness of breath, and lung irritation , spread of the drug into the environment possibly affecting people other than the one taking the drug , and contamination of the device used for nebulization particularly when the device is reused and inadequately cleaned.
Using the device properly helps prevent side effects. Drugs applied to the skin are usually used for their local effects and thus are most commonly used to treat superficial skin disorders, such as psoriasis Psoriasis Psoriasis is a chronic, recurring disease that causes one or more raised, red patches that have silvery scales and a distinct border between the patch and normal skin.
A problem with the immune Although many bacteria come in contact with or reside on the skin, they are normally unable to establish an infection Common fungal skin infections are caused by It is one of the most common reasons people see doctors who specialize in skin disorders dermatologists.
Itching makes people want to scratch. See also Itching. Normal skin owes its soft, pliable texture to its water content. To help protect against water loss, the outer layer of skin contains oil The drug is mixed with inactive substances. Depending on the consistency of the inactive substances, the formulation may be an ointment, cream, lotion, solution, powder, or gel see Topical Preparations Topical Preparations Topical drugs drugs applied directly to the skin are a mainstay of treating skin disorders.
Systemic drugs are taken by mouth or given by injection and are distributed throughout the body Some drugs are delivered bodywide through a patch on the skin. In such cases the use of liquids or soluble formulations may be helpful.
Many drugs, however, are not stable in solution for liquid formulation and in such cases careful consideration should be given to the option of switching to alternative drug treatment. Difficulties frequently arise with patients who are prescribed modified-release preparations as these must not be crushed or broken at the point of administration.
Modified-release formulations can delay, prolong or target drug delivery. The aim is to maintain plasma drug concentrations for extended periods above the minimum effective concentration. For patients, their main advantage is that doses usually only need to be taken once or twice daily. Damage to the release controlling mechanism, for example by chewing or crushing, can result in the full dose of drug being released at once rather than over a number of hours.
This may then be absorbed leading to toxicity or may not be absorbed at all leading to sub optimal treatment. Nurses should seek advice from a pharmacist or the prescribing doctor if they are uncertain about a formulation of solid dose forms and whether or not they are suitable for crushing. The sublingual mucosa offers a rich supply of blood vessels through which drugs can be absorbed.
This is not a common route of administration but it offers rapid absorption into the systemic circulation. The most common example of sublingual administration is glyceryl trinitrate in the treatment of acute angina. These are aimed at particular markets where taking tablets may be problematic, such as the treatment of migraine rizatriptan where symptoms of nausea may deter patients from taking oral treatments. The formulation is also used to treat conditions where compliance with prescribed drug regimens may be problematic, for example, olanzapine used to treat schizophrenia can be administered by the sublingual route.
The rectal route has considerable disadvantages in terms of patient acceptability in the UK at least and unpredictable drug absorption but it does offer a number of benefits.
It offers a valuable means of localised drug delivery into the large bowel, for example the use of rectal steroids in the form of enemas or suppositories in the treatment of inflammatory bowel disease. Antiemetics can be administered rectally for nausea and vomiting and paracetamol can be give to treat patients with a pyrexia who are unable to swallow.
The topical application of medicines has obvious advantages in the management of localised disease. The drug can be made available almost directly at the intended site of action, and because the systemic circulation is not reached in great concentration, the risk of systemic side-effects is reduced. For example:. Topical administration has also become a popular way of introducing drugs into the systemic circulation through the skin. The development of transdermal patches that contain drugs began with the introduction of a hyoscine-based product for the treatment of nausea in the early s.
Rectal medication may be in suppository form or in liquid form to be administered as a retention enema. Unlike the oral route, drugs with irritant or unpalatable nature can be administered through the rectum. Rectal route can also be preferred when the patient has persistent vomiting or is unable to swallow.
Also, this route can be used for systemic drug administration in addition to the local administration. Drugs are applied topically, that is to the skin or mucous membrane of the eye, ear, nose, mouth, vagina, etc. This route provides a high local concentration of the drug without affecting the general circulation. However, drugs that are absorbed into the circulation after local administration may then have systemic effects.
Drugs for topical applications are usually available as creams, ointments, liniments, and drops. Drugs administered through this route must be highly lipophilic. Absorption via this route is slow but conducive to producing long-lasting effects. Special slow-release matrices in some transdermal patches can maintain steady drug concentrations that approach those of constant IV infusion.
Transdermal patches also provide less absorption problems in the gastrointestinal tract that are commonly experienced by patients who take oral medications.
Drugs administered through this route include fentanyl patches for severe pain management, nitroglycerin transdermal patch used to prevent episodes of angina in people who have coronary artery disease, nicotine patches for cessation of smoking, etc.
Drug delivery by inhalation is a common route, both for local and for systemic actions. This delivery route is particularly useful for the direct treatment of asthmatic problems, using both powder aerosols e.
Drugs may be inhaled as gases e. This is the method of administration of volatile anesthetics such as ether, halothene, and methoxyflurane.
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